My experiences with .223 AICS mags:
1) Original AI poly mag (now discontinued): Worked great out of the gate but after a few sessions rounds started to dive, a lot. Got rid of the mag.
2) MDT poly mags: Damn these things have some stiff springs in them. They have mostly fed well though, requiring a good hard push given the springs, most times I have had them out. Occasionally, it seems mostly on very cold days, they want to nose up the occasional round though. In these cases the round will jam on the face of the barrel above the chamber. Also, the MDT poly mags are physically large, bigger than the metal MDT .308 / 6.5 CM mags I have so many of. I have encountered a chassis and bottom metal they don't fit in so some users may encounter an issue. Fortunately, the chassis and bottom metals they haven't fit did not happen to be the ones I use on my .223, they were on other AICS pattern mag rifles so it didn't end up an issue for me. I expect I will eventually sell both the MDT poly mags I have. They require a bit more vigorous running of the bolt than I prefer and when they rarely misfeed this interacts with the fairly light neck tension on my reloads to stove rounds. I just don't trust them. Of course, being poly mags, I am also hesitant to try to alter anything about the feed lip geometry as that usually doesn't go well with poly and would probably just wreck the mag.
3) Accurate mag lined metal .223 mag: Yikes, this thing is expensive. It also protrudes from the mag well significantly further than other mags. That being said, not one misfeed so far. At this point I am really only using that Accurate mag because it feeds easily and smoothly and I trust it. Last couple rounds do go in a bit stiffer than the first bunch but it works fine with all 10.
I have one of the new MDT metal mags on order that I picked up on black friday and am also excited to try that out. I am aware of just one more .223 AICS mag type in existence, the Magpul AICS Pmag. I have not yet tried this one at this time either.
I should also note that my .223 has a standard chamber and so I haven't paid any attention to mag COAL as none of my rounds is loaded long enough for that to matter. They would not fit in the chamber if they were.
Lastly, it seems from what I have read that .223 AICS mags and how they interact with a particular rifle can be a bit idiosyncratic, so my experiences should not be necessarily translated as applicable to your rifle. Bottom line, I would recomend getting one of each and selling what you don't like. Want to buy a couple poly MDT's?